Ultra-sonic distance sensor system and method with correction feature for sensor value

Abstract

An ultra-sonic distance sensor system includes means for measuring the elapsed time between transmission of ultra-sonic waves and receipt of the return wave reflected by an object which reflects ultra-sonic waves and the distance to which is to be measured. A correction value is derived on the basis of the rate of change of the signal level of a receiver signal output by an ultra-sonic receiver. On the basis of the derived correction value, the resultant distance value or the measured elapsed time value is corrected to ensure accurate measurement of the distance to the object can be ensured. This allows more precise height control for a vehicle when the distance detector is applied to a height control system of an automotive vehicle.

What is claimed is: 
     
       1. An ultra-sonic distance sensor comprising: an ultra-sonic wave transmitter for transmitting ultra-sonic waves of a given frequency toward an object at regular intervals;   an ultra-sonic receiver for receiving ultrasonic waves reflected by the object and producing a receiver signal having a value indicative of the amplitude of the received ultra-sonic waves;   first means for measuring the elapsed time between transmitting of the ultra-sonic waves by said transmitter and reception of ultra-sonic waves having an amplitude greater than a predetermined level, said first means producing an elapsed-time-indicative signal having a value representative of the measured elapsed time;   second means for detecting the rising characteristics of the receiver signal and deriving a correction value for said elapsed-time-indicative signal value on the basis of the detected rising characteristics of the receiver signal; and   third means for modifying said elapsed-time-indicative signal value in accordance with said correction value, deriving a distance value indicative of the distance to said object based on the modified-elapsed-time indicative signal value, and producing a distance-value-indicative signal representative of the derived distance value.   
     
     
       2. The distance sensor as set forth in claim 1, wherein said second means latches the peak value of said receiver signal and derives the correction value on the basis of the latched peak value. 
     
     
       3. The distance sensor as set forth in claim 2, wherein said second means comprises a peak-hold circuit associated with said receiver to receive said receiver signal and latch the peak value thereof, and a correction value generator which outputs a correction-value indicative signal which is derived on the basis of the latched peak value. 
     
     
       4. The distance sensor as set forth in claim 3, wherein said correction value is derived from a correction table which holds correction values in a one-to-one correspondence with the peak values of the receiver signal. 
     
     
       5. The distance sensor as set forth in claim 1, wherein said second means derives said correction value on the basis of the rate of change of the receiver signal while signal level is rising. 
     
     
       6. The distance sensor as set forth in claim 5, wherein said second means measures the period of time required for the receiver signal level to rise from a first given level to a second given level. 
     
     
       7. The distance sensor as set forth in claim 6, wherein said second means includes a correction table which holds a predetermined correction value for each value of said period of time. 
     
     
       8. A method for measuring the distance to an object by means of ultra-sonic waves comprising the steps of: triggering an ultra-sonic wave transmitter to transmit ultra-sonic waves at a given frequency towards said object;   starting a timer concurrently with triggering of the ultra-sonic wave transmitter;   receiving ultra-sonic waves reflected by said object and producing a receiver signal having a signal level proportional to the amplitude of the received ultra-sonic waves;   terminating measurement of elapsed time by said timer and producing a timer signal indicative of the measured elapsed time concurrently with production of said receiver signal;   detecting signal level variation characteristics of said receiver signal and deriving a correction value for said timer signal value on the basis of detected variation characteristics;   modifying said timer signal value in accordance with said correction value; and   performing arithmetic operations on the basis of said modified timer signal value to derive a distance value indicative of the distance to said object and producing a signal indicative of said distance value.   
     
     
       9. The method as set forth in claim 8, in which said correction value is derived on the basis of the peak value of said receiver signal. 
     
     
       10. The method as set forth in claim 8, in which said correction value is derived on the basis of the period of time required for said receiver signal level to vary from a first given level to a second higher given level.